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Standard XII

Physics

Momentum

A rail road c...

Question

A rail road car is moving with a constant acceleration of $1$ $m / s^{2}$ . A block of $5$ kg is put on a horizontal rough floor in the car. At time $t = 0$ , velocity of the car is $5$ m/s. Considering friction is sufficient and block is not slipping on the floor, the work done on the block by friction force (as observed from ground frame) during $t = 0$ to $t = 2$ sec will be (coefficient of friction is $μ_{s}$ ):

60

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10

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600 μ_{s}

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None of these

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Solution

The correct option is A $60$ J
seudo force acts on the block placed on a car...
$F_{s e u d o} = m a$ ( $a$ is accleration of a car)
Now since the block is not slipping therefore friction is sufficient to balance the suedo force....
$f_{f r i c t i o n} = F_{s e u d o} = 5 N$
During $t = 0$ to $t = 2 s e c$ , displacement of car is
$S = u t + .5 a t^{2}$
$S = 12 m (a = 1 m / s^{2}, u = 5 m / s, t = 2)$
Work done by friction
$60 J$

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